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Many medical and surgical patients experience pain. Surgery causes tissue damage leading to the release of local chemical mediators that stimulate pain fibres. In addition direct damage to nerves can cause pain. Ischaemia, obstruction, infections, inflammation and joint disease also cause pain. Cancer is an important cause of pain. Pain may be induced by movement, which is sometimes unavoidable, e.g. the thorax and abdominal wall when breathing. In contrast, immobility can cause pain due to pressure sores and joint stiffness. In addition, a patient’s perception of pain is altered by many factors, including the patient’s overall physical and emotional well-being, cultural background, age, sex and ability to sleep adequately. Depression and fear often worsen the perception of pain.
Tissue damage causes a nociceptive pain, which can be further divided into a sharp, stabbing pain, which is conveyed by the finely myelinated Aδ fibres, and a dull, throbbing, ‘slow’ pain, which is conveyed by the larger non-myelinated C fibres. Nociceptive pain is usually acute, tends to resolve as tissue heals and responds well to opioid analgesia. Injury or abnormal function within the nervous system causes neuropathic pain. It is felt as an area of burning or a shooting pain. It may be triggered by non-painful stimuli such as light touch, so-called allodynia. Examples of causes include postherpetic neuralgia, peripheral neuropathy, e.g. due to diabetes, and phantom limb pain. Neuropathic pain is often difficult to treat, partly because of its chronic but episodic na-ture and it is less responsive to opiates. Most of the time, pain has both nociceptive and neuropathic components.
The principal reason for treating pain is to relieve suffering. It improves patients’ ability to sleep and their overall emotional health. However, good pain control can also have other benefits: postoperatively it can imp-prove respiratory function, increase the ability to cough and clear secretions, improve mobility and hence reduce the risk of complications such as pneumonia and deep vein thromboses. This allows a faster recovery.
To diagnose and then treat pain first requires asking the patients about their pain. Often, if pain is treated aggressively and early, it is easier to control than when the pa-tent becomes distressed and exhausted. Patients should be asked to score their pain on a scale from none to very severe (sometimes a 10-point scale is useful, where 0 represents no pain and 10 the worst imaginable pain). In some cases where verbal communication is not possible or difficult, a visual scale of 1–10 or pictures of faces representing degrees of pain is useful. They should be asked what precipitates pain, such as movement or breathing, and whether the pain prevents or interrupts sleep. It is important to establish whether the pain is nociceptive, neuropathic or both. Often there is more than one pain and these may require separate treatment plans.
In a patient who is already taking analgesia, it is usefull to assess their current use, the effect on pain and any sideeffects. The patient should also be asked about his or her beliefs about drugs they have been given before. The patients should be involved as far as possible in the managreement of their pain. Adverse effects such as nausea and constipation are predictable, patients should be alerted to these and provided with means by which these can be treated early.
The World Health Organization analgesia ladder is a method for choosing appropriate analgesia depending on the severity of pain. It was originally developed for cancer patients but is useful for many types of pain. Initially, analgesia may be given on an as needed basis, but if frequent doses are required, regular doses should be given, so that each dose is given before the effect of the previous dose wears off. A combination of different drugs often improves the pain relief with fewer adverse effects. After analgesia is initiated, if it is ineffective at maximal dose, the next step on the ladder is tried. Certain drugs are contraindicated or used with caution in patients with comorbidities. Postoperative patients may descend the ladder, as severe pain is expected immediately after tissue damage and this pain reduces as healing takes place.
STEP 1 (Mild pain): Non-upload analgesia is used, such as paracetamol or an NSAID. These may be given orally or rectally.
STEP 2 (Mild to moderate pain): Weak opioids such as codeine, dihydrocodeine or tramadol orally or intra-muscularly are added to regular paracetamol or an NSAID.
STEP 3 (Moderate to severe pain): Strong opioid analgesia such as morphine or diamorphine is used.
The oral route is preferred for most patients, but for patients unable to take oral medication or for rapid relief of acute pain, intramuscular or intravenous boluses are faster acting and more suitable. The disadvantage of boluses for continued pain is that often there is a delay between the patient experiencing pain and analgesia being given. In intensive care settings or terminal care a continuous infusion by a syringe driver may be appropriate, but with any continuous delivery system there is a risk of accidental overdose, so regular monitoring of pain score, sedation score and respiratory rate is needed. In stable patients with severe ongoing pain, a transdermal patch may be suitable. These release opioid in a controlled manner, usually over 72 hours.
Patient-controlled analgesia (PCA) is a system by which the patients can determine the frequency of dosing of their analgesia. A loading dose is given first, then the patient presses a button to deliver subsequent small boluses of intravenous opioid. The PCA pump has a lock-out time usually set at 5–10 minutes, which allows time for each dose to take effect before another dose can be given. This prevents respiratory depression due to accidental overdose by the patient repeatedly pressing the button. If the patient becomes overly sedated, the delivery of opioid ceases. If patients are not adequately analgesed, the bolus dose is increased. This system is not suitable for patients who are too unwell or confused to understand the system and be able to press the button.
Local anaesthetic is useful perioperatively. It is often given around the wound or as a regional nerve block to provide several hours of pain relief. Spinal anaesthesia is useful for surgery of the lower half of the body. Postoperatively, continued analgesia using an epidural catheter to administer boluses or a continuous infusion is useful. Usually a combination of local anaesthetic with an opioid is used. The advantage of epidural analgesia is that there is good pain control with a lesser risk of the systemic side-effects of opioids. However, complications include hypotension due to sympathetic block, urinary retention and motor weakness. Patients require specialist care and monitoring on a ward accustomed to the management of patients with epidurals.
These are other drugs that are not primarily analgesics, but can help to relieve pain. In particular, neuropathic pain is relatively insensitive to opioids; drugs such as antidepressants and anticonvulsants are more effective, e.g. amitryptiline or gabapentin. Tramadol is a weak opioid that has some action at adrenergic and serotonin receptors and so may be useful for combination nociceptive and neuropathic pain. Muscle spasm often responds to benzodiazepines.
In addition to prescribing analgesia, it is important to consider other methods that relieve pain, such as treating the underlying cause, immobilising a painful joint with a splint, mobilising joints for stiffness and treating concomitant depression. Acupuncture, local heat or ice, massage and transcutaneous electrical nerve stimulation (TENS) can often help with pain.
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